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Water balance after closing a plaster pool?

Evening folks,

Just wondering if anyone checks their water balance after closing. I've been playing around with PoolMath and it seems that as the temps get lower the water drifts towards the iffy zone for plaster pools.

Re: Water balance after closing a plaster pool?

Normally, when the water temperature drops, the pH rises and that compensates for the CSI to keep it fairly stable. Of course, other things can happen to move the pH, but the temperature effect would have the pH rise when the temperature drops and then the pH would drop again when the temperature rose back up.

With the water being so cold you don't need to worry as much about the CSI for plaster since any negative effects would be very slow (within reason -- the pH shouldn't drop very much even if it did for some reason).

Re: Water balance after closing a plaster pool?

Originally Posted by chem geek

Normally, when the water temperature drops, the pH rises and that compensates for the CSI to keep it fairly stable. Of course, other things can happen to move the pH, but the temperature effect would have the pH rise when the temperature drops and then the pH would drop again when the temperature rose back up.

With the water being so cold you don't need to worry as much about the CSI for plaster since any negative effects would be very slow (within reason -- the pH shouldn't drop very much even if it did for some reason).

Thanks for the reply Chem Geek. Makes me feel better. I guess I got a little carried away with PoolMath, but with a major investment in our backyard, I'd rather err on the safe side.

Re: Water balance after closing a plaster pool?

Vinyl pools react differently from plaster and cement based pools. You may find that the pH rises slowly over time in plaster pools.

I suggest that you check the pH once a month to make sure it doesn't go higher than 8.0. If the pH goes over 8.2, then scaling is possible.

Thanks onBalance. Appreciate the input. The pH goes from about 7.5 to 7.8 every 3 days. I add about a 1/3 of a jug of acid, and the cycle starts again in a few days. So, I guess we should be ok, but I will take your advice and check every so often.

BTW, thank you for the post on bi-carb startup. I convinced our builder to use that when we started to fill. Although, he wouldn't bite on the entire process (fearing warranty issues) we did follow about 80% of your suggestions.

Re: Water balance after closing a plaster pool?

Once the water temperature lowers to very cold temperatures and/or a pool cover is placed over the pool, then the pH rise will slow down a lot and won't need testing and adjusting as often as it does now.
So just to be clear, my first response was based on closing the pool and very cold or freezing water temperatures.

Re: Water balance after closing a plaster pool?

Originally Posted by onBalance

Once the water temperature lowers to very cold temperatures and/or a pool cover is placed over the pool, then the pH rise will slow down a lot and won't need testing and adjusting as often as it does now.
So just to be clear, my first response was based on closing the pool and very cold or freezing water temperatures.

Our cover is a mesh cover not a solid. Will that matter? Temps are already dropping the 40's overnight, so the water temp should be pretty low once we close. We're having one more hurrah this weekend, running the heater, and I'll turn off the heater to the pool for the season.

Re: Water balance after closing a plaster pool?

A mesh cover will allow the water to lose carbon dioxide, which means that the pH will rise faster than if the cover was solid vinyl.
Therefore, you may want to test the pH more frequently than I suggested earlier. Perhaps once a week during winter time.

Re: Water balance after closing a plaster pool?

Originally Posted by onBalance

A mesh cover will allow the water to lose carbon dioxide, which means that the pH will rise faster than if the cover was solid vinyl.
Therefore, you may want to test the pH more frequently than I suggested earlier. Perhaps once a week during winter time.

At the risk of stating the obvious, the mesh cover (which I also have), since allowing water to pass through it, will have an impact on water chemistry. With my newly replastered pool last winter, I had to adjust the pH probably 7-8 times and would have continued but of course at some point the water froze. Strangely, my pH has continued to go up over the past few months, and this really should no longer be attributable to the plaster. So I'll probably wind up doing the same this winter. My goal is always to keep the SI as close to zero as possible. Being on the alkaline side is safer than being negative. You can always take it off (scale) but you can't put it back on (etching).

Re: Water balance after closing a plaster pool?

Originally Posted by onBalance

A mesh cover will allow the water to lose carbon dioxide, which means that the pH will rise faster than if the cover was solid vinyl.
Therefore, you may want to test the pH more frequently than I suggested earlier. Perhaps once a week during winter time.

Re: Water balance after closing a plaster pool?

Originally Posted by three4rd

At the risk of stating the obvious, the mesh cover (which I also have), since allowing water to pass through it, will have an impact on water chemistry. With my newly replastered pool last winter, I had to adjust the pH probably 7-8 times and would have continued but of course at some point the water froze. Strangely, my pH has continued to go up over the past few months, and this really should no longer be attributable to the plaster. So I'll probably wind up doing the same this winter. My goal is always to keep the SI as close to zero as possible. Being on the alkaline side is safer than being negative. You can always take it off (scale) but you can't put it back on (etching).

Thanks three4rd. Your post now makes me think about the portion of water that's not frozen. Wouldn't the pH continue to rise under the frozen portion? According to the post by onBalance and Chem Geek it could continue to rise albeit slowly.

Re: Water balance after closing a plaster pool?

The pH won't rise from outgassing under the ice since no significant amount of gas should be able to escape. The pH rise could still occur from plaster or other sources, but at such cold temperatures that should be fairly slow. It's a moot point since there's not much one can do about it. So long as it doesn't rise so much as to induce calcium carbonate scaling or metal staining, it doesn't matter.